Technical Reference Notes
AEO_ALO04/12/20/25x48 Series
(Single Output 8th Brick)
Input Filter for FCC Class B Conducted Noise
A reference design for an input filter that can provide FCC Class B conducted noise levels is shown below (See Figure 61).
Two common mode connected inductors are used in the circuit along with balanced bypass capacitors to shunt common mode
currents into the ground plane. Shunting noise current back to the converter reduces the amount of energy reaching the input
LISN for measurement.
The application circuit shown has an earth ground (frame ground) connected to the converter output (-) terminal. Such a
configuration is common practice to accommodate safety agency requirements. Grounding an output terminal results in much
higher conducted emissions as measured at the input LISN because a hard path for common mode current back to the LISN is
created by the frame ground. “Floating” loads generally result in much lower measured emissions. The electrical equivalent of
a floating load, for EMI measurement purposes, can be created by grounding the converter output (load) through a suitably
sized inductor(s) while maintaining the necessary safety bonding.
FILTER
PARTS LIST
CKT CODE DESCRIPTION
CTX01-15091
Common
Cooper Electronic
Mode Choke
Technologies
X-Cap
Y-Cap
Cin
0.47 µF X 4pcs
22 nF X 4 pcs
220µF X 1pc
Figure 61: Class B Filter Circuit
MODEL: AEO_ALO04/12/20/25x48 SERIES
AUGUST 25, 2005 - REVISION G
SHEET 23 OF 26
ASTEC [ Astec America, Inc ]
